1. Field of the Invention
The present invention relates to an axial flow fan, and more particularly, to an axial flow fan that is suitable for use as a cooling device for cooling electronic equipment.
2. Description of the Related Art
In recent years, an increased amount of heat is generated from apparatuses such as personal computers and servers as the capabilities of constituent electronic components are improved. Servers, in particular, contain a number of electronic components within relatively small housings, and thus the temperature within the housings rises significantly. Since normal operating temperature ranges are defined for many of the electronic components, the electronic components are unable to fulfill their functions properly outside their temperature ranges. For this reason, a cooling device with a high cooling performance is necessary in order to cool the electronic components. As such a cooling device, axial flow fans are conventionally used.
Meanwhile, due to the reduction in size of the apparatuses such as personal computers and servers in recent years, a plurality of electronic components are densely arranged within the housings of such apparatuses. The cooling devices for cooling the housings are therefore required to be reduced in size while ensuring a large air volume. As a possible measure, a large air volume is obtained by rotating the motor of a conventional axial flow fan at a high speed.
In order to rotate a motor at a high speed, it is necessary to apply a high voltage to the coils in the motor, or to pass a high current through the coils. However, the method of applying a high voltage to the coils necessitates a booster circuit for raising the supply voltage, which leads to an increase in costs. The method of passing a high current through the coils brings about an increase in heat generated in the coils, which leads to lowering the motor efficiency.